The present invention relates to implantable devices, and more particularly to a multiple reservoir implantable pump that may be designed to allow different constant flow rates and bolus injection capability.
Implantable pumps have been well known and widely utilized for many years. Typically, pumps of this type are implanted into patients who require the delivery of active substances or medication fluids to specific areas of their body. For example, patients that are experiencing severe pain may require painkillers daily or multiple times per day. Absent the use of an implantable pump or the like, a patient of this type would be subjected to one or more painful injections of such medication fluids. In the case of pain associated with more remote areas of the body, such as the spine, these injections may be extremely difficult to administer and particularly painful for the patient. Furthermore, attempting to treat conditions such as this through oral or intravascular administration of medication often requires higher doses of medication and may cause severe side effects. Therefore, it is widely recognized that utilizing an implantable pump may be beneficial to both a patient and the treating physician.
Many implantable pump designs have been proposed. For example, U.S. Pat. No. 4,969,873 (“the '873 patent”), the disclosure of which is hereby incorporated by reference herein, teaches one such design. The '873 is an example of a constant flow pump, which typically include a housing having two chambers, a first chamber for holding the specific medication fluid to be administered and a second chamber for holding a propellant. A flexible membrane may separate the two chambers such that expansion of the propellant in the second chamber pushes the medication fluid out of the first chamber. This type of pump also typically includes an outlet opening connected to a catheter for directing the medication fluid to the desired area of the body, a replenishment opening for allowing for refilling of medication fluid into the first chamber and a bolus opening for allowing the direct introduction of a substance through the catheter without introduction into the first chamber. Both the replenishment opening and the bolus opening are typically covered by a septum that allows a needle or similar device to be passed through it, but properly seals the openings upon removal of the needle. As pumps of this type provide a constant flow of medication fluid to the specific area of the body, they must be refilled periodically with a proper concentration of medication fluid suited for extended release.
Implantable pumps may also be of the programmable type. Pumps of this type provide variable : flow rates, typically through the use of a solenoid pump or a peristaltic pump. In the solenoid pump, the flow rate of medication fluid can be controlled by changing the stroke rate of the pump. In the peristaltic pump, the flow rate can be controlled by changing the roller velocity of the pump. However, both of these types of programmable pumps require intricate designs and complicated controlling mechanisms. As such, it is more desirable to utilize pumps having designs similar to the aforementioned constant flow pumps.
Nonetheless, the benefit of providing a variable flow rate pump, or at least a pump having the capability of multiple fixed flow rates, cannot be forgotten. While a constant flow of medication such as a painkiller may indeed be useful in dulling chronic pain, there may be times when a patient may require additional pain relief. With a constant flow pump, the flow rate is fixed, so the physician or medical professional may only provide such relief by direct injections of painkillers and the like through the aforementioned bolus port (which provides direct access to the afflicted area), or by increasing the overall active substance concentration of the fluid housed in the pump. While indeed useful, the former amounts to nothing more than additional injections, something the pump is designed to circumvent. In addition, the latter may be considered less convenient for the physician or medical professional, since it requires choosing a different concentration of medicine, rather than merely adjusting the flow rate of the already present medication via an external programmer, as would be done with a programmable pump.
In addition, pumps are known that normally act in a fashion similar to the aforementioned constant flow type pumps, but that also allow for a patient controlled bolus dose. These pump types are sometimes referred to as Patient Controlled Actuation (“PCA”) pumps. One example of such a pump is disclosed in U.S. Pat. No. 6,283,944, the disclosure of which is hereby incorporated by reference herein. During periods of regular pain or the like, PCA pumps provide a constant flow rate of medication fluid to a patient. However, during periods of heightened pain, a PCA pump may be actuated by a patient to provide an additional medication injection. Essentially, this allows for a bolus injection, in line with that described above, without the need for the use of a needle or syringe. PCA pumps also typically include a safety mechanism for preventing a patient from overdosing themselves. While such designs may be beneficial in light of standard constant flow type implantable pumps, nevertheless, such designs are often complicated and bulky.
Therefore, there exists a need for an implantable constant flow pump, which allows for multiple fixed flow rates and may be configured to allow for patient controlled bolus doses or the like.